High yield bio diesel fuel preparation process

ABSTRACT

An improved biodiesel fuel preparation process using the step of simultaneous separation of biodiesel reaction product and glycerin, by specific gravity separation taking advantage of the pressure created by the heavier glycerin by using density loops, drawing of by-product glycerin from the bottom of the container while drawing off the lighter biodiesel reaction product from the top of the container as it is forced out by the density loop pressure. All of this is without the use of any pumps thereby reducing energy consumption and cost. Process efficiency is achieved by separating the methanolysis into two steps.

FIELD OF THE INVENTION

This invention relates to biodiesel fuel formed from vegetable oils and animal fats, either as first use or recycled.

BACKGROUND OF THE INVENTION

Diesel fuels are traditionally hydrocarbon liquids obtained by fractionating and refining of petroleum. The cost of petroleum crude has risen rapidly and these rather rapid price increases in crude oil costs have placed a severe burden upon many commercial and industrial operations using substantial amounts of diesel fuel.

Diesel fuel is typically produced through a refining and distillation process from crude petroleum oils. Crude petroleum oils contain the entire range of fuel components from methane and propane to gasoline to diesel fuel to asphalt and other heavier mixture components. The refining process separates the crude oil into mixtures of its constituents, based primarily on their volatility. Diesel fuels are on the heavy end of a barrel of crude oil. This gives rise to diesel fuel's high BTU content and power.

All diesel fuel injection equipment has some reliance on diesel fuel as a lubricant. The lubricating properties of diesel fuel are important, especially for rotary and distributor type fuel injection pumps. In these pumps, moving parts are lubricated by the fuel itself as it moves through the pump—not by the engine oil. Other diesel fuel systems—which include unit injectors, injectors, unit pumps, and in-line pumps are partially fuel lubricated. In these systems the mechanism typically consists of a plunger or needle operating in a sleeve or bore, where the fuel is used to lubricate the walls between the reciprocating piece and its container. The lubricity of the fuel is an indication of the amount of wear or scarring that occurs between two metal parts covered with the fuel as they come in contact with each other. Low lubricity fuel may cause high wear and scarring and high lubricity fuel may provide reduced wear and longer component life. For many years, the lubricity of diesel fuel was sufficient to provide the protection needed to maintain adequate performance. Recent changes (1993 and beyond) in the composition of diesel fuel, primarily the need to reduce fuel sulfur and aromatic levels, and the common chemical process used to accomplish these changes (called hydro-treating) have inadvertently caused the removal of some of the compounds that provide lubricity to the fuel. There is therefore a need to enhance diesel fuel lubricity.

In addition, another property of diesel fuel that has been given considerable attention over the years is its cold flow properties. At very low temperatures of operability, diesel fuel is subject to cold flow impacts. That is, it may gel or crystallize. These properties which need improvement have over the years provided an incentive to investigate alternative sources of diesel fuel such as biodiesel.

Biodiesel is a clean burning alternative diesel fuel produced from domestic renewable sources such as vegetable oils. It contains no petroleum-based product but can be blended at any level with petroleum based diesel to create a biodiesel blend of varying properties commonly used to overcome some of the inherent disadvantages of petroleum diesel. In particular, biodiesel is defined as the mono alkyl esters of long chain fatty acids derived from vegetable oils or animal fats, for use in compression-ignition (diesel) engines. Preparation of biodiesel per se is not new, see for example, Journal of American Oil Chemists Society, Vol. 57, No. 11, November 1980 entitled “Searching for New Diesel Fuels”. However, while vegetable oils in general and soy oil in particular have been used in the past to prepare biodiesel, there always is a continuing need for increased preparation efficiency to achieve the best economics.

The general process of preparing biodiesel from soybean oil involved reacting soybean oil, which is a mixture of a long chain fatty acid esters of glycerin, with the most common fatty acids being palmitic, stearic, oleic, linoleic and linolenic, with methanol, using sodium methylate (commonly prepared by mixing methyl alcohol and sodium hydroxide) as a catalyst, to provide soybean methyl esters of a typical average molecular weight of the soybean oil methyl ester being about 292.2. A typical soybean oil methyl ester profile of the reaction product is as follows: Typical Profile Weight Fatty Acid Percent Mol. Wt. Formula Palmitic 12.0 270.46 C₁₅H₃₁CO₂CH₃ Stearic 5.0 298.52 C₁₇H₃₅CO₂CH₃ Oleic 25.0 296.50 C₁₅H₃₃CO₂CH₃ Linoleic 52.0 294.48 CH₃(CH₂)₄CH═CHCH₂CH═CH(CH₂)₇CO₂CH₃ Linolenic 6.0 292.46 CH₃(CH₂CH═CH)₃(CH₂)₇CO₂CH₃

The by product of the methanolysis process is glycerin which is simultaneously formed along with the methyl esters of the fatty acids. Glycerin too is a valuable product that can be separated and sold to further advance the economics.

A measure of the efficiency of a biodiesel process is how close the reaction is to stoichiometric ratios of ingredients. For example, if the process uses 100 lbs of soybean oil the stoichiometric amount of methanol would be 10 lbs of methanol. This would provide 100 lbs of fatty acid methyl esters and 10 lbs of glycerin if the yield is 100%. Most biodiesel processors use 60-200% more methanol than is required by the reaction stoichiometry to achieve a complete reaction.

Another measure of the efficiency of soybean methyl ester preparation is measuring the energy consumption per gallon. Energy consumption, of course, occurs during the reaction operation in the form of electrical costs, heating costs, pumping costs, etc. This invention achieves as one of its significant advantages a significant reduction in energy consumption by eliminating some pumps from a biodiesel continuous processing system, with this being accomplished by taking advantage of the difference in specific gravity of the product biodiesel and the product glycerin, to achieve a gravity separation while at the same time using the pressure created by the heavier glycerin to force the biodiesel out so that it can be drawn off the top of a reaction tank without the need for any centrifugal pumps. This lowers energy consumption and is an advantage.

Another advantage of the present invention is that it is a fairly low cost unit operation to build and it can be run continuously or as a batch process at the discretion of the operator. The average hold time within the system being about 14 hours from introduction to finished B-100 biodiesel.

Another object of the present invention is to provide a high quality biodiesel from soybean oil which can be effectively blended with diesel from petroleum sources in order to provide desirable quality fuel blends that decrease the risk of gelling in cold weather and which provide enhanced lubricity for the petroleum diesel fuel.

Yet another object of the present invention is to provide high quality B-100 soy biodiesel which meets all ASTM standards by a process which is close to achieving stoichiometric efficiency.

The method and manner of accomplishing each of the above advantages and objectives, as well as others, will become apparent from the Detailed Description of the Invention which follows hereinafter.

BRIEF SUMMARY OF THE INVENTION

An improved biodiesel fuel process which involves the step of simultaneous separation of biodiesel reaction product and glycerin reaction product from a container of the mixed products by specific gravity separation, drawing off by-product glycerin from the bottom of the container through a density loop to create pressure so that biodiesel reaction product can be drawn off from the top of the container, all without the use of pumps in this part of the system. This reduces energy consumption and cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of the process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As heretofore mentioned, biodiesel is defined as mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats which conform to ASTM D6751 specifications for use in diesel engines. Biodiesel refers to the pure fuel before blending with diesel fuel. Biodiesel blends are denoted as “BXX” with “XX” representing the percentage of biodiesel contained in the blend (i.e., B20 is 20% biodiesel, 80% petroleum diesel) and B-100 as 100% biodiesel.

Looking at FIG. 1, which shows a flow chart 10 for the process, the entrance to the process is on the left side of FIG. 1; the finished product B-100 exits on the right side of FIG. 1. Soybean oil (bleached and deodorized) is purchased and filled in to storage tank 12 and pumped via pump 14 through a filter assembly and adjustable flow control valves to dryer and dryer heat exchanger 16 and then into a first reactor, or container, or tank 18. First reactor tank 18 can be a 600 gallon tank and the flow rate into it may vary from, for example 2-6½ gallons per minute. Heat exchanger 16 heats the oil to a temperature of 135° F. to 140° F. and it is maintained at that temperature range in the first reactor 18. Hot soy oil is pumped from the heat exchanger 16 via line 17 into reactor 18. Methanol is pumped from tank 20 via line 22 and pump 24 through tube mixer 26 via line 28 into reactor 18. Sodium hydroxide from catalyst container 30 is pumped via line 32 into tube mixer 26 wherein it mixes with methanol from tank 20 and moves via line 28 moves into reactor 18 as a premixed methanol/sodium methylate catalyst. The amount of sodium methylate i.e. sodium hydroxide and methanol pumped into reactor 18 is 80% of the amount needed for the reaction with the amount of soybean oil pumped into reactor 18. It has been found most efficient, and it is a part of this invention, to separate the reaction into a major part and a minor part. When the reaction to convert soybean oil to biodiesel is separated into two parts in a first reaction with the majority portion of the sodium methylate/methanol mix and a second reaction in a second container with a minor portion of the sodium methylate/methanol mix better yields are obtained. The amount of sodium methylate/methanol mix in the first reactor can vary but can be from 75% to 80% of the stoichiometric amount and is preferably 80% of the a stoichiometric amount. The reaction time in reactor 18 can vary but will generally be within a range of two to three hours residence time in tank 18 at a flow rate of 2½ gallons/minute. Tank 18 has a mixer (not depicted).

The mixed reaction product (biodiesel and glycerin) is moved to settling tank 34 via line 33. Settling tank 34 may be a 1900 gallon tank. In settling tank 34 the residence time can vary from 2½ to 3 hrs. Glycerin settles to the bottom of the tank 34 because its specific gravity is heavier than biodiesel which rises to the top. As more mixed reaction product moves in, the glycerin settles to the bottom and crude biodiesel being lighter rises to the top. As a result, the gravity separated glycerin moves down and out via line 36, and passes through the density loop 38 to the crude glycerin tank 40. The density loop 38 is of a correct height to create sufficient pressure that the crude biodiesel is forced out of the glycerin settling tank 34. The biodiesel moves out without any pumping action via line 42 as it is displaced through the addition of the mixed reaction product. It moves via line 42 into the second reactor 48. Also introduced via tube mixer 44 into the second reactor 48 is the minor portion of the sodium methylate/methanol mix. It can be from 20 to 25% of the amount required for stoichiometric reaction. Likewise a residence time here is approximately 2½ hours but can be from 2 to 3 hours with the temperature being within the range of 135° F. to 140° F. The product then moves via line 50 to the second glycerin settling tank 52. Here again, the difference in specific gravity is taken advantage and glycerin is drawn off from the bottom via line 54 through density loop 55 to crude glycerin tank 40. Crude biodiesel after reacting with the second 20% of the catalyst and methanol is drawn off at the top of tank 52 via line 56 again without the need for any pump system since it is maintained at an elevation caused by the glycerin density loop 55. Thereafter, the biodiesel goes to a wash spray system wherein it may be washed multiple times. As depicted in FIG. 1 one wash is shown with 25% (hydrochloric acid) add to the water spray wash to keep the pH within the range of 7 to 8. Acid is introduced to the wash via tank 58 after leaving mixer 57. Water is also introduced via line 60 with the scrubbing water washing action taking place in tank 62. The biodiesel again is moved off from the top via line 64, without any pump since density loop 63 keeps pressure in the system. It is washed again in tank 68, using pressure from density loop 72. Wash water and soap removal occurs via line 70 and the lower density biodiesel is drawn off at 74 to test tank 76. It is then dried at dryer 78. Refined washed and dried B-100 is then ready for shipment, as indicated at storage tanks 80, 82 and 84.

Certain process conditions here are worthy of mention. Vacuum is maintained in dryers 16, 78 at about 29 inches of mercury. This is accomplished by a conventional hot water aspirator, such as a liquid rig vacuum pump.

Importantly and worthy of specific mention is to note that in the first and second reactors 18 and 48 and the glycerin settling tanks and wash tanks no pumps are used to remove the material from the settling tank and wash tanks. The density loops use the specific gravity difference to create a pressure head to move the material without use of pumps.

Yields of greater than 90% and often 98%, based on the input weight of oil, are achieved in the process of the present invention and energy consumption is down such that the cost per gallon of produced biodiesel is significantly reduced.

The B-100 can be mixed with petroleum diesel to compose 2% to 20% of the blend (B2 to B20) to achieve better lubricity, better cold weather impact and greater engine efficiency. It therefore can be seen that the invention accomplishes at least all of its stated objectives. 

1. In the process of preparing biodiesel fuel from vegetable oils, the improvement comprising: separating biodiesel reaction product in a container from the simultaneously formed reaction by-product glycerin without the use of any pumps or the energy necessitated by use of pumps, by employing a density loop to create pressure, while drawing the glycerin from the bottom of a container and pushing biodiesel off from the top of the container.
 2. The process of claim 1 wherein the reaction occurs in two containers, one with the major portion of the alcohol-sodium methylate reaction component and the other with the minor portion of the alcohol-sodium methylate reaction component.
 3. The process of claim 2 wherein the major portion is from about 75% to about 80% of the methylating agent and the minor portion from about 25% to about 20% of the methylating agent.
 4. The process of claim 3 which uses acid washing steps to maintain the pH within the range of 7-8 and to wash soap from the biodiesel reaction product.
 5. The process of claim 4 when the process is continuous.
 6. The process of claim 5 wherein B-100 biodiesel is recovered at 98% yield or higher. 